function Food(el){
    this.el=el
    this.len=20
    this.foodObj = null
    this.foodX = 0
    this.foodY = 0
}
Food.prototype.create = function(){
    let divObj=document.createElement('div')
    divObj.style.width = this.len+'px'
    divObj.style.height = this.len+'px'
    divObj.style.background='green'
    divObj.style.position='absolute'
    this.foodObj=divObj
  
    this.el.appendChild(divObj)
    this.move()
}
Food.prototype.move=function(){
    let foodXMaxNum = this.el.clientWidth/this.len-1
    let foodYMaxNum = this.el.clientHeight/this.len-1
    this.foodX=Math.floor(Math.random()*(foodXMaxNum+1))*this.len
    this.foodY=Math.floor(Math.random()*(foodYMaxNum+1))*this.len
    console.log(this.foodX)
    console.log(this.foodY)
    this.foodObj.style.left = this.foodX+'px'
    this.foodObj.style.top = this.foodY+'px'
}